Researchers estimate that by 2015 almost 75 percent of American adults will be obese.

But how do they determine whether a body is underweight, healthy, overweight, or obese?

In this lesson we’ll explore the body mass index, or BMI, which uses height and weight measurements to help determine whether a person is at a “healthy” weight. We’ll use this formula to find out the weight statuses of celebrities, from Taylor Swift to Arnold Schwarzenegger, and discuss whether BMI is all it’s cracked up to be.

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